affecting the Potato-crojis. 103 



before I discovered them in the vessel in which the tuber was 

 placed^ as well as multitudes of smaller flies, all of which I will 

 now describe. 



The whole belong to the Order Diptera: the first I shall 

 notice is included in the Family Tipulid^, and the Genus 

 PsYCHODA, and has been named 



29. P. nervosa (fig. 47 ; r, the natural size*). The males are 

 twice as large as the females ; they are ashy-white, clothed with 

 longish wool: the little head is buried under the thorax: the 

 black eyes are large and lunate: the 2 horns are as long as the 

 thorax and composed of 1 J (?) small joints, black at the base, giving 

 them an annulated appearance : the abdomen is short and of a 

 dirty colour : the 2 wings when at rest meet over the back slanting : 

 they are iridescent, very large, oval, and lanceolate, with numerous 

 longitudinal hairy nervures : the entire margin is also hairy ; 

 balancers small, clubbed, and white : 6 legs woolly ; the feet 

 5-jointed, the tips black. Length ^, expanse 3 lines. 



In February, 1846, the larvoe and pupae were abundant in the 

 rotten potatoes, also in decaying leaves and dunghills, and the 

 flies have been bred by Mr. Haliday from putrescent fungi. 

 These flies sometimes swarm in outhouses and about drains in 

 spring and autumn. 



The larvae are not \ a line long, yellowish-white, cylindrical, 

 spindle-shaped, with 11 distinct annulations besides the head, 

 which is triangular ; the tail is elongated and tubular. The pupa 

 is about ^ oi ^ line long, ochreous, and ferruginous ; it is elongate- 

 ovate in repose (fig. 48, the back ; 49, the underside ; s, the natural 

 size), but the body can be stretched out and attenuated when 

 disturbed, as in fig. 50: from the forehead project 2 slender 

 appendages, like horns, on either side are laid the short stout 

 antennae, and the wings meet over the breast, with the legs 

 stretched out between them : the abdominal segments are ciliated 

 and the tail is forked. 



Several species of a little swarthy two-winged fly were bred 

 from the decaying potatoes in multitudes. They are called 

 Sciara by Meigen, and Molohrus by Latreille. The larvae I 

 received from Mr. Graham : they are slender worms, about a 

 quarter of an inch long, whitish and opake, but when immersed in 

 water they become perfectly transparent, exhibiting the ochreous 

 viscera and the food digesting in the stomach ; when in motion 

 they taper towards the head, which is oval, horny, black and 

 shining; the body is composed of 13 segments with 7 or 8 spi- 

 racles on each side ; the tail is broad and rounded, but slightly 

 pointed in the centre (fig. 51 ; t, the natural size). The pupa is 



* Curtis's Guide, Genus 1151, No. 6, and Brit. Ent., fol. and pi. 745. 



